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The axial distance the nut advances in one revolution of the screw. The lead is equal to the pitch times the number of starts.

When compared to general-purpose thread forms, centralizing threads are manufactured with tighter tolerances and reduced clearance on the major diameter.

On an acme screw, this diameter is approximately halfway between the land diameter and the root diameter. It is the diameter at which the thread thickness is equal to the space between threads.

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Lead accuracy is the difference between the actual distance traveled versus the theoretical distance traveled based on lead. For example: A screw with a 0.5 inch lead and 0.004 inch per foot lead accuracy rotated 24 times theoretically moves the nut 12 inches.

CAUTION - Although a side load will not cause a centralizing thread to wedge, the nut is not designed to operate with a side load such as a pulley, drive belt, etc. See "Load Definition" section for further information.

NOTE: Nook Industries acme screw designations reference major diameter and effective turns per inch. For example: ¼" -4 RH requires four turns for one inch of travel. A ¼" -4 RH has 4 starts and a 0.062" pitch.

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There are three main classes of Acme thread forms: General Purpose (G), Centralizing (C), and Stub Acme. The General Purpose and Centralizing thread forms have a nominal depth of thread of 0.50 × pitch and have a 29° included thread angle. Some Nook sizes have 40° included angle. Trapezoidal thread forms have a 30° included thread angle.

If an acme nut is side loaded with a radial load, a "G" class will "wedge" when the nut thread flanks come in contact with the screw thread flanks. To prevent wedging, less clearance and tighter tolerances are allowed between the major diameter of the nut and the major diameter of the screw.

The acme thread form, established over 100 years ago, replaced square thread screws, which had straight sided flanks and were difficult to manufacture.